Radioactivity is the release of energy from the decay of the nuclei of certain kinds of atoms and isotopes. Atomic nuclei consist of protons and neutrons bound together in tiny bundles at the center of atoms. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. Radioisotopes: Isotopes are atoms of the same element that differ from each other because they have different numbers of neutrons. Many elements have one or more isotopes that are radioactive. This means they have unstable nuclei that give off... Show more

Radioactivity is the release of energy from the decay of the nuclei of certain kinds of atoms and isotopes. Atomic nuclei consist of protons and neutrons bound together in tiny bundles at the center of atoms.

A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay.
Radioisotopes: Isotopes are atoms of the same element that differ from each other because they have different numbers of neutrons.
Many elements have one or more isotopes that are radioactive. This means they have unstable nuclei that give off radiation. Radioactive isotopes are called radioisotopes. An example of a radioisotope is carbon-14. All carbon atoms have 6 protons, and most have 6 neutrons. These carbon atoms are called carbon-12, where 12 is the mass number (6 protons + 6 neutrons). A tiny percentage of carbon atoms have 8 neutrons instead of the usual 6. These atoms are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 atoms are unstable because they have too many neutrons.
To be stable, a small nucleus like carbon, with just 6 protons, should have a 1:1 ratio of neutrons to protons. In other words, it should have the same number of neutrons as protons. In a large nucleus, with many protons, the ratio should be about 2:1 or even 3:1 neutrons to protons for the nucleus to be stable. In elements with more than 83 protons, all the isotopes are radioactive. The force of repulsion among all those protons overcomes the strong force holding them together. This makes the nuclei unstable.
Elements with more than 92 protons have such unstable nuclei that these elements do not even exist in nature. They exist only if they are created in labs.

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